1. Field of the Invention
The present invention relates to cooling apparatuses for internal combustion engines and motorcycles including the cooling apparatuses.
The present application claims priority to Japanese Patent Application No. 2013-108639 filed in Japan on May 23, 2013, the entire contents of which are hereby incorporated by reference.
2. Description of the Related Art
A water-cooling cooling apparatus is conventionally known as an apparatus for cooling an internal combustion engine of a motorcycle. A cooling apparatus of this type includes a radiator, water piping through which the radiator and an internal combustion engine are connected to each other, a water pump that conveys cooling water, and a thermostat that adjusts a temperature of the cooling water. The cooling water flows through the internal combustion engine and the radiator in sequence. The cooling water increases in temperature by cooling the internal combustion engine, and decreases in temperature by radiating heat through the radiator. The thermostat is operated to reduce a flow rate of the cooling water when the temperature of the cooling water is low, and increase the flow rate of the cooling water when the temperature of the cooling water is high. The flow rate of the cooling water to be supplied to the internal combustion engine is adjusted in this manner, thus keeping the temperature of the cooling water within an appropriate range.
When the internal combustion engine is started up, it is desirable to warm the internal combustion engine promptly from the standpoint of fuel efficiency improvement, for example. In order to warm the internal combustion engine promptly, the flow rate of the cooling water flowing through the radiator is preferably reduced so that the amount of heat radiated from the cooling water is decreased. For example, in a conventionally known cooling apparatus for an internal combustion engine, a flow rate of cooling water flowing through a radiator is reduced during a warming up operation.
FIG. 3-2 of JP 2007-2678 A discloses a cooling apparatus in which a flow rate of cooling water flowing through a radiator is reduced during a warming up operation of a motorcycle. As illustrated in FIG. 16A, a cooling apparatus 300 disclosed in JP 2007-2678 A includes a radiator 301, a water pump 302, a thermostat 303 connected to a suction port of the water pump 302, and an oil cooler 304. The cooling apparatus 300 further includes a main passage made up of a passage 306 through which a discharge port of the water pump 302 and an internal combustion engine 305 are connected to each other, a passage 307 through which the internal combustion engine 305 and the radiator 301 are connected to each other, and a passage 308 through which the radiator 301 and the thermostat 303 are connected to each other. The cooling apparatus 300 further includes an oil cooler passage 309 made up of a passage 309a through which the passage 306 and the oil cooler 304 are connected to each other, and a passage 309b through which the oil cooler 304 and the radiator 301 are connected to each other. The cooling apparatus 300 further includes a bypass passage 310 through which the passage 307 and the thermostat 303 are connected to each other.
At the time of startup of the internal combustion engine 305, the internal combustion engine 305 has a low temperature, and therefore, the cooling water has a low temperature. When the temperature of the cooling water is low, the thermostat 303 operates to shut off communication between the passage 308 and the passage 306 so as to block circulation of the cooling water through the main passage. As a result, the cooling water flows as indicated by arrows in FIG. 16A. Specifically, the cooling water discharged from the water pump 302 is distributed so that some of the cooling water passes through the internal combustion engine 305 and the remainder of the cooling water passes through the oil cooler 304. The cooling water that has passed through the internal combustion engine 305 and the cooling water that has passed through the oil cooler 304 then merge with each other, and the merged cooling water flows through the bypass passage 310 and subsequently returns to the water pump 302 via the thermostat 303.
Upon lapse of a certain period of time from the startup, the temperature of the internal combustion engine 305 increases, and therefore, the temperature of the cooling water increases. When the temperature of the cooling water is high, the thermostat 303 operates to shut off communication between the bypass passage 310 and the passage 306 and allow communication between the passage 308 and the passage 306. As a result, the cooling water flows as indicated by arrows in FIG. 16B, and the cooling water circulates through the main passage. Specifically, the cooling water discharged from the water pump 302 is distributed so that some of the cooling water flows through the internal combustion engine 305 and the remainder of the cooling water passes through the oil cooler 304. The cooling water that has passed through the internal combustion engine 305 and the cooling water that has passed through the oil cooler 304 then merge with each other, and the merged cooling water flows through the radiator 301 and subsequently returns to the water pump 302 via the thermostat 303.
However, the cooling apparatus 300 requires the bypass passage 310 through which the cooling water flows only during a warming up operation, in addition to the main passage through which the cooling water is supplied to the radiator 301 and the oil cooler passage 309 through which the cooling water is supplied to the oil cooler 304. Hence, the number of components of the cooling apparatus 300 is increased, which contributes to an increase in cost. For motorcycles, there is a strong demand for weight reduction of vehicle-mounted components. However, the cooling apparatus 300 has difficulty in achieving weight reduction because the bypass passage 310 cannot be removed therefrom. Moreover, motorcycles are subject to considerable constraints in terms of piping layout. The cooling apparatus 300 is likely to complicate piping layout because the bypass passage 310 has to be additionally disposed.